Resistance

High Dark Resistance

Medium Fire and Magic Resistance

Low Lightning Resistance

Can be poisoned

Can bleed

Attack Patterns

Light Vertical Cleaver: One of his faster moves, he raises his left arm quickly in the air then smashes it down in a short range towards the player. This move can either be a single action or be chained into 3 quick consecutive strikes. Will only do this if the player is in range. The horizontal tracking of each swipe isn't that great, but because there are a series of attacks in quick succession it ends up tracking pretty well.

Hard Vertical Cleaver: A move almost solely reserved for players at range, he raises his cleaver in the air, smashing it down in a long range attack towards the player. This move is rather deceiving in nature as it has a tendency to move forward after the strike makes contact with the ground. Is capable of hitting players up to 1/3rd of the room away but it cannot be chained. Tracks extremely well, the boss will practically turn 180° to face a target.

Horizontal Cleaver: Moving his cleaver to his side, he sweeps 170° in front of him. It cannot be chained. Not much tracking, just a huge amount of coverage.

Fist Smash: Similar to the Light Vertical Cleaver attack, he raises his balled fist in the air and smashes it towards the player. This move has quicker start up than any cleaver attack and will send the player flying away. It cannot be chained. Does not track horizontally very well.

Fist Grab: Moving his open hand to his left side he attempts a sweeping grab motion 150° in front of him. If it connects with the player, he will grab and wring them over his mouth dealing massive damage (iIf your vigor is low, you will be killed outright). Poor timing while dodging left can result in the grab to connect after the dodge motion is finished. It cannot be chained nor does it track horizontally very well.

Dual Side Smash: Slams the ground directly to his sides with first the left hand, then the right, regardless of which side you're currently on. Because it has no tracking and a long animation, it is very easy to dodge and punish with multiple hits.

Has occurred before half health

Oil Vomit: If this attack hits you it will douse you in oil. If you then step into the fire periodically throughout the boss arena, you will combust violently and will be knocked onto your feet and take a large amount of damage. It is easy to avoid and even easier to avoid the effects though so this attack should not be too much of a danger.

Only Occurs After Half Health

Dark Energy Explosion: Slouching into himself, he creates a ball of dark energy from his core and after a second releases a blast in every direction. Blast radius is about two back rolls, and will cause unshielded affected players with a guard broken-esk stunned effect. It cannot be chained.

Dark Energy Cleaver Wave: Pulling his cleaver to his side, he infuses it with dark energies and thrusts it at the player. Similar to the Hard Vertical Cleaver attack, he almost solely reserves this move for players at range. The wave releases from the end of the cleaver 45° towards the player. It cannot be chained.

Strategy

While his motions are extremely telegraphed, his damage is extremely punishing.

Melee Strategy

His attacks are slow and have a long cool down, so the player will have plenty of time to recover, though the player must be aware to avoid the Fist Grab attack. His ranged attacks are his slowest by far, so backing far away is a fine option if the player is in need of healing.

By far the best melee strategy for this boss is moving in a straight line forwards and backwards rather than circling around him. Keep your shield up, provoke an attack by moving towards him, and step backwards out of range, rushing forwards to strike at his cleaver arm at the end of his attack. After dealing the arm enough damage, it will be cut off. The Rotten will still attempt to attack with his missing limb, completely ineffectively, leaving him open to attacks. The limb will regrow shortly afterwards, however.

Ranged Strategy

Stay close enough to The Rotten where you can roll away from his attacks then fire off your spells or arrows. Make sure to pay attention to where the burning ponds are, because they will kill you as often as the boss will, if you're not careful enough.

Alternatively, try keeping your distance. He is resistant to Dark magic, but sorceries do decent damage. At medium or long range, he will mostly try to do the heavy overhand cleaver to come after you, but if you're far enough away, he won't even come close to hitting you The only thing you really have to watch for is the dark energy cleaver attack, which has an extremely obvious tell, and you can run towards him to get behind. Mostly you just need to watch our for the pools of fire, and that he doesn't corner you.

Pyromancy will work wonders on him as well, but requires getting in closer, which puts you more at risk. You'll be spending a lot more time and stamina dodging attacks than you would be further away.

Notes

Both of his arms can be chopped off, though they will regenerate. When both arms are gone the only attack you need worry about is his dark energy explosion - which is not much of a problem, as he keeps himself busy swinging his useless stubs trying to hit you. The cleave arm drops after around 1300 - 1500 damage has been dealt to it.